I'm new to diabetes, but at buffets in general I find it helps to eat "expensive" instead of indulgent. So I'd target the expensive proteins and nice veggies available, and leave the cheap carbs behind. Fish, seafood, nice cuts of meat, etc.
Carbs and sweets are very cheap for cruises to serve, so it's a bit of a rip-off to fill up on them when you can pack in more of the quality proteins instead. The satisfaction of getting the most financial advantage out of the meal might help offset missing out on the carb indulgence.